I'm running into this issue as well. Using Truncheon my EC runoff is coming out at 3.2 when they are going in at 1.4. I'm in week 7 and my runoff seems quite low for most of my trays except the closest one (gets most runoff/water). I guess I will flush tomorrow with RO water... do I ph that going in? I been reading all sorts of things suggesting minimize ph down in coco. Below is a pic of my close tray, then after that are pics of the necrosis I been getting on other trays with less runoff with the high EC.
Ur not gonna get an accurate reading from your runoff till you filter the crud.
I catch my runoff and filter it w a doubled up pantyhose then check it.
In my opinion you should do a slurry test instead. Salt builds up over time and if your not flushing with 3× the amount of coco, i.e 3gl pot, 9 gl of h20 @ least every 4 weeks your runoff is going 2 reflect the amount of salt in the bottom of the pot and rootzone. You may finish the run but lockout of 1 form or another is eminent.